Analog-to-digital converters (ADC's) are vital for effective signal processing. Known ADC's use electrical or radio frequency-based technology, but rapid advances in technology that require greater processing speeds, increased channel bandwidths and improved transmission reliability, have resulted in a steadily growing focus on the optical domain and the vast potential therein. Optical ADC's are relatively new when compared to electrical and radio frequency (RF)-based processing.
One approach to perform rapid optical analog-to-digital conversion is by angular deflection of a laser beam. In such a system, a laser generates a beam of light in response to an input analog signal. The intensity of the beam depends on the analog input signal. The beam is deflected by an intensity-discriminating material, such as a silicon prism. The index of refraction of the silicon prism is modified in accordance with the intensity of the beam. Because the beam intensity varies as the analog input signal varies, the beam is deflected by the prism over a range of angles. A plurality of light detectors are positioned to detect the deflected beam and provide a digital output signal. If two light detectors are used, for example, the intensity-discriminating material deflects the beam toward one of the two light detectors based upon the intensity of the beam. In this manner, a digital signal can be created from an analog signal.
For some optical ADC designs, the angular deflection through the intensity-discriminating material may be small. If the beam is not sufficiently deflected by the intensity-discriminating material, it may not be possible to variably direct the beam toward a sufficient number of light detectors to create a desired digital signal. Extending the path length of the deflected beam will compensate for the small angle of deflection and will achieve a lateral deflection of the beam that is sufficient to be used with the plurality of light detectors. Due to design considerations, however, it may not be possible to lengthen the path length as much as is necessary. For example, some applications may limit the space available for an ADC, and a long path length may not fit within the given space requirements. A custom optical lens design could be used to partially shorten the required path length, but this could add considerable cost and complexity to an ADC design. Furthermore, in applications such as avionics where space is at a premium, such a lens design would not completely resolve the issue of a long path length requirement.
It is therefore an object of the invention to lengthen the path of a light beam, such as a laser beam, in a relatively compact space.
It is another object of the invention to provide a beam-lengthening apparatus that is compact enough to be used in space-critical applications such as avionics.
It is another object of the invention to provide a beam-lengthening apparatus that is simple and inexpensive to manufacture.
A feature of the invention is an apparatus having a plurality of reflective surfaces disposed within an at least partially enclosed chamber and arranged so that a light beam directed into the chamber reflects a plurality of times between the reflective surfaces before emerging from the chamber.
An advantage of the invention is a simple and inexpensively manufactured beam path lengthener that is compact enough to be used as part of an optical analog-to-digital converter in avionics and other space-critical applications.